Gotchas: as you might now, bhyve's fbuf device accepts the vga option (e.g. vga=off etc), and different guest OSes might require different settings to make things work. It's not possible to change this using libvirt right now, so the default value (which is vga=io) is used, hence some guests will not work.

Kudos to Fabian Freyer for doing the majority of that work as a part of GSoC 2016.